U.S. Pat. Nos. 4,660,329 and 4,986,036 disclose power sanders having air driven motors including a housing containing a chamber through which pressurized air is directed, and a rotor contained in the housing and driven rotatively by the air. A shaft extends vertically through a central passage in the rotor and is driven by the rotor and acts in turn to power a shoe carrying sandpaper for abrading a work piece. The shaft is journalled for rotation in the housing by bearings carried by upper and lower walls of the housing, and is connected to the rotor by a key acting to transmit rotary motion between the rotor and shaft.
One problem which has been encountered in motors of this general type results from the tendency for the rotor to move slightly relative to the driven shaft when repeatedly subjected to very high starting and stopping torques and other unpredictable and varying forces during a sanding operation. This relative shifting movement of the rotor and contained shaft, though initially very slight, gradually increases over a period of time causing the shaft, the passage in the rotor through which the shaft extends, and the key to wear progressively and allow increasing relative motion of the parts ultimately resulting in such damage to the rotor and shaft and housing walls as to require their replacement. The above mentioned patents show an arrangement for reducing this wear by providing a leaf spring radially between the rotor and key for yieldingly urging the rotor transversely of the axis of the device relative to the shaft and key and thereby resisting relative displacement of these parts when the motor is operating.